A microwave signal is mainly used in communications of satellite communication equipment, base stations of cellular phones and the like, and one of devices used in processing of the microwave signal is a circularly polarized wave generator. The circularly polarized wave generator converts a linearly polarized wave into a circularly polarized wave and, as a well-known configuration thereof, there is a corrugated circularly polarized wave generator (see, e.g., Patent Document 1).
The corrugated circularly polarized wave generator disclosed in Patent Document 1 is a rectangular waveguide, and a plurality of pleat-like protrusions (corrugates) orthogonal to an axial direction are arranged at predetermined intervals in the axial direction on opposing wall surfaces. In addition, the heights of the individual protrusions are varied such that an envelope represented by the tips of the protrusions forms a smooth quadratic or cubic Cos curve with the center in the axial direction serving as the vertex. With the arrangement of the protrusion described above, a passing phase difference occurs between two linearly polarized waves (V-polarized wave, H-polarized wave) input to the circularly polarized wave generator that are orthogonal to each other, and the linearly polarized waves are converted into a circularly polarized wave (clockwise wave, counterclockwise wave) in a predetermined frequency band.